Continuous flow thermal machines and in particular in ram-jets and turbojets



March 8, 1960 A. MESTRE 2,927,427

CONTINUOUS FLOW THERMAL MACHINES AND IN PARTICULAR IN RAM-JETS AND TURBO-JETS Filed July 18, 1955 Y s Sheets-Sheet 1 N VENT R xyvd (grime v ATTUHNEY March 8, 1960 A. MESTRE I 2,927,427

CONTINUOUS mow THERMAL MACHINES AND IN PARTICULAR IN RAM-JETS AND TURBO-JETS Filed July 18, 1955 3 Sheets-Sheet 2 INVENTDR ATTDHNEYS March 8, 1960 MEsTRE 2,927,427

- CONTINUOUS FLOW THERMAL MACHINES AND IN PARTICULAR IN RAM-JETS AND TURBO-JETS Filed July 18, 1955 3 Sheets-Sheet 3 INVENTDR 5 I v ATTDHNEYS United tates atent CONTINUOUS FLOW THERMAL MACHINES AND IN gARTICULAR IN RAM-JETS AND TURBO- JET Andr Mestre, Chatiilon-sonsd3agneux, France, assignor to Ofiice National dEtudes et de Recherches Aeronautiques 0.N.E.R.A., Chatillon-sons-Bagneux, France, a French society Application July 18, 1955, Serial No. 522,622

. Claims priority, application France May 10, 1955 i 9 Claims. ((11. till-39.82)

The present invention relates to continuous flow thermal machines, this expression including all thermal machines through which passes a continuous or practically continuous gaseous stream of comburent gas (air flow ing at high speed) and into which fuel is injected in at least one zone called injection zone, ignition of the mixture of the comburent gas and fuel and stabilization of the flame being. obtained, downstream of the injection zone, by a device for continuously producing a pilot'flame. My invention is more especially concerned with jet engines, in particular for aircrafts, which are to 'include means for stabilizing the main combustion flame," which is the case of ram-jets and also of turbojets or turbo-propellers the thrust of which is increased by a post-burner system working by supplementary injection of fuel into the stream of hot gas downstrea of the main combustion zone.

The object of my invention is to provide a thermal machine as above described which is better adapted to meet the requirements of practice than those existing at the present time.

It consists chiefly in providing such a machine with at least one continuous pilot flame generator including a combustion chamber separated from the gaseous stream whereignition is to be produced by a partition along which said stream is flowing and which extends in the general direction of said stream at least in the zone where the mixture of fuel and comburent gas is already formed, said partition being provided in said zone with at least one elongated slot extending in the general direction of flow, whereby the pilot flame generating device produces, through said slot, a flame in the form of a sheet located in a plane passing through said slot and through a'fstraight line at right angles both to said slot and to the direction of flow of the gaseous stream.

Preferred embodiments of my invention will be hereinafter described with reference to the accompanying drawings, given merely by way of example and in which:

' Fig. 1 is a diagrammatic perspective view with parts cut away of the rear portion of a ram-jet made accordiugto the invention.

Fig. 2 is a cross sectional view on an enlarged scale of an injector belonging to this ram-jet.

Fig; 3 is a perspective view on an enlarged scale and with parts cut away, of a pilot combustion device helonging to said ram-jet.

"'Fig. 4 is aperspective view with parts cut away of the post-burner system of a turbo-jet, this system being made according to the present invention.

jjFig. 5 is a partial perspective view of a modification of the system of Fig. 4. ,Fig. 6 is a perspective view with parts cut away showing the construction of "one of the elements of the device of Fig. l. i

.. .Fig. 7 is a a partial perspective view of still another modification. V y

My invention will now be described in its application to a jet engine, such as a ram-jet or a turbo-jet provided with a post-burner system, including a central body the rear portion of which forms a streamlined point and which limits, together with the casing of the engine, an annular passage through which flows a gas: eous stream containing fuel mixed therewith, in which gaseous stream is to be produced and stabilized a flame substantially at the level of said streamlined point or slightly behind it. t

The engine includes a casing 1, for instance of cylindrical shape, in which is mounted a central body 2 the rear portion of which forms a streamlined point 2a, said central body 2 determining, together with the wall of easing 1, an annular passage A through which flows a gaseous stream fed with fuel by a main feed device. This main feed device consists for instance of a plurality of radial arms 3 distributed in a section of the annular passage A and fixed both to casing l and central body 2, each of these radial arms being provided with a plurality of injection orifices 3a preferably directed along lines making an angle of about 60 in the upstream direction with the direction of flow of the gaseous stream, as shown by Fig. 2. These injection orifices 3a thus form one or several rows of injection means coaxial with envelope 1 and streamlined point 2a.

According to my invention, the means for igniting the fuel mixture and stabilizing the flame downstream of the main feed device 3 are made as follows:

A pilot combustion chamber is provided in casing 1 so as to be separated from annular passage A (through which circulates the gaseous stream to be ignited) by a wall along which said stream flows, said wall extending in the general direction of the flow at least in the portion located downstream of the main feed device 3.

Said wall is provided in the above mentioned zone with at least one elongated slot 4 extending in the general direction of the gaseous flow.

In this way, ignition of the fuel mixture circulating in annular passage A is obtained by means of a pilot flame gushing out through said slot in a radial direction substantially perpendicular to the direction of flow of the gaseous stream, this pilot flame therefore forming a kind of sheet starting from said slot and passing through a line starting from said slot and at right angles to the direction of flow of the gaseous mixture.

In the particular case of a jet engine provided with a central body 2, the wall which is to separate the pilot combustion chamber from annular passage A is the wall of said central body 2 itself.

In other words, advantage is taken of the presence of said central body 2 in casing 1 and of the fact that the wall of said central body serves to guide the gaseous stream in a zone where said stream has already been fed with fuel (said wall being theretore parallel to the general direction of flow of said stream), and the pilot combustion device is mounted inside said central body 2 so as to cooperate with the gaseous stream to be ignited by means of one or preferably several slots 4 advantageous distributed at equal intervals in the wall of said central body 2.

In this way, the pilot ignition device and flame stabilizing means do not produce any supplementary drag in the gaseous stream.

Furthermore, due to the axial position of the pilot device and to the radial direction of the sheets of pilot flames produced through slots 4, I obtain a deep erle-1 trationof the pilot flames into the gaseous stream to tion and maintaining of the main combustion.

be ignited, which is ofcourse favorable to the producdependently controlling the flow rate of the pilot fuel and that of the main fuel injected through orifices 3a. Such distinct valve means are diagrammatically shown on Fig. 1 at S for the pilot fuel and at 6 for the main fuel.

The fact that the two fuel circuits are independent makes it possible, in particular, to start the pilot igniting means and to adjust the pilot combustion even when the valve means 6 which control the main feed device 3 are closed.

I will now proceed to a more detailed description of the embodiment illustrated by Figs. 1 to 3. This 'construction corresponds to a ram-jet engine but the same arrangement might be used in the case of a turbo-jet engine.

The injection of the pilot fuel into central body 2 is preferably performed as shown by Fig. 3 by means of an injector 7 of the eddy-forming type which supplies a substantially conical sheet of small droplets substantially coaxial with streamlined point 2a.

The comburent air is introduced into streamlined body 2 in a manner which will be hereinafter specified and which may vary according to the kind of engine that is considered. Instead of directly sending the whole of said air onto the conical sheet of pilot fuel, at least a portion thereof is caused to pass through an air distributing air device 8 provided for this purpose around pilot injector 7 and arranged in such manner as to give rise to a plurality of air streams directed toward said conical sheet of pilot fuel.

Such an air distributor 8 may be constituted for instance by a kind of funnel the apex of which is located slightly upstream of injector 7 and the base of which, opened in the downstream direction, preferably has a diameter smaller than that of central body '2 (or of streamlined point 2a which forms an extension of said body) at the level of said base, the wall of said funnel being provided with a plurality of orifices 9 advantageously distributed to form at least one row near the base of the funnel.

Thus, a portion of the comburent air is directed through the orifices 9 toward the sheet of pilot fuel, the remainder of the air passing between the base of funnel 8 and the wall of the central 'body '2.

The igniting means for the pilot fuel are preferably housed in funnel 8, said means consisting for instance of an electric spark plug 10 close "to the wall of said funnel and preferably immediately upstream of the row of orifices 9. p

The slots 4 through which the radial pilot flames extend are advantageously provided on their edges with fins 11 extending radially from streamlined structure 2a toward casing 1 and the radial height of which increases in the downstream direction, this height preferably remaining always smaller than one third of the distance existing 'in every section between the corresponding walls of part 2a and of casing 1.

Such fins serve on the one hand to facilitate the shaping "and sharp penetration of the pilot flames into the gaseous stream and, on the other hand, contribute in stiffening body 2a in a portion thereof where slots 4 might weaken it. v

Said slots may be located downstream of the main injection device '3 which is itself preferably located slightly downstream of the base of streamlined portion 2a, the length of the slots 4 preferably ranging from .'1 to 1.5 times the diameter of the central body 2 (diameter of the base of the streamlined point 2d).

"When slots 4 are so positioned and dimensioned, it is advantageous to place their upstream end in a plane where the diameter of the streamlined point 2a ranges from 1 to 0.6 times'the diameter of the central body '2 and their downstream end in a plane where the diameter of the streamlined point 2a ranges from {0.8 to 0.5

Advantageously, the number of slots 4 is one half of that of the main radial injectors 3. In this case, each slot is preferably located in the wake of a radial arm. Therefore, every second radial arm will be followed by a slot, the next radial arm being located in the interval between two slots.

It should be noted that it is advantageous, in order to avoid risks of burbling behind the streamlined point 20 when the main combustion is taking place, to give said streamlined point a length at least equal to three times the diameter of its base. Therefore, in the case of an existing engine where the said streamlined point does not comply with this condition, it may be come necessary to modify the shape of said point by fitting an extension thereon.

I will now describe how the comburent air necessary for the pilot combustion is collected, the devices necessary for this being established in accordance with the characteristics of the jet engine that is considered.

In the case of a ram-jet (as shown by Figs. 1 to 3), this air will be advantageously collected by providing an annular air intake P facing the upstream direction and preferably having a streamlined leading edge so as to avoid unstability both of the external flow (in annular passage A) and of the internal flow (toward the pilot cornbustion chamber).

Preferably the cross section of the air intake will range from /6 to 2 of the cross section of the annular passage A in the plane of said air intake. Furthermore, there should be a relation between the cross section of the air intake and the total area of slots 4, said area ranging for instance from five to eight times that of said air intake cross section.

When the pilot combustion device belongs to a postburner system disposed downstream of the turbine 12 of a turbo-jet engine (case of Fig. 4), air for pilot combustion may be collected by means of the dynamic air in takes P provided in the leading edge of the streamlined radial arms 13 extending between the external casing 1 of the engine and the streamlined point 2a. In this case also, it will be advantageous to comply with the conditions above stated concerning the ratio between the cross section of the air intake, the cross section of the annular passage A in the same plane and the total area of slots 4.

Means may be provided for closing said air intakes B; when the post-burner system is not in action and such means may be for instance constituted by valve means 14 connected to a common control through rods 15.

In the case of a post-burner system for a turbo-jet engine, I may also, according to a modification diagrammatically illustrated by Fig. 5, collect the comburent air for the pilot combustion from the compressor of the turbo-jet engine, this air being then fed toward the pilot combustion chamber through conduits 16 which pass through radial arms 13. In this case also, valve means may be provided so as automatically to control the flow of said air according as the post-burner system is in or out of action.

It should be noted that in the last mentioned arrangement (Fig. 5), the feed of air under pressure to the pilot combustion chamber will facilitate the penetration of the pilot flames flowing out through slots 4 into the annular gaseous stream flowing in space A.

I will now describe an advantageous construction of the streamlined point 2a which is to contain the pilot device. I

Such a construction is illustrated 'by "Fig. 6. In this case there are two distinct elements a and b to constitute the portions of streamlined point 2a extending respectively upstream of slots 4 and downstream thereof.

The intermediate portion of said streamlined point 24 is constituted by 'a plurality of gutter-shaped elements having a width corresponding to the distance between two successive slots -4, the edges ot-"said gutters serving to constitute the above referred to fins 11.

.' In order to connect the ends, of saidgutter-shap'ed elements c.with elements a and b, I provide ring-shaped members d provided with a middle rib. Said rings are secured to the corresponding elements a or b and gutters c are fixed to said rings, preferably by electric welding either by spots or continuous;

Thus there will be provided between two consecutive gutters c an interval corresponding to the desired width of slots 4.

With such a construction, the streamlined point 2a is very rigid and well adapted to support high temperatures. Furthermore its weight is relatively small. The constitutiveelements. of said structure may be made of steel sheets, for instance of a thickness averaging 3 of a millimeter.

Fig. 7 corresponds to a modification in which both the shape of the body in which pilot combustion is to take place and the way in which afuel mixture is fed to said body are difierent from what has been described above. In this case the streamlined body 20, instead of being centrally disposed as in the preceding embodiments, is in the form of an annular structure obtained by revolving about the longitudinal axis of easing 1 (not visible on Fig. 7) a symmetrical biconvex airfoil section. This structure 20 is carried by casing 1 by means of radial arms 13. The fuel mixture serving to pilot combustion is the same as that flowing through the main casing 1. It penetrates into annular body 20 through a slot 21 extending along the leading edge of said annular body 20. Inside this hollow body and behind said intake slot 21, there is provided a fiat ring 22 perpendicular to the general direction of the stream passing through said hollow body and leaving between its edges and the inner wall of the inner body, a sufiicient space for the flow of the fuel mixture. This ring 22 is fixed inside the hollow body 20 by means of flexible plates 23 extending parallel to the direction of the stream and fixed to the leading edge of body 20, these plates 23 extending frontwardly of said leading edge so as to be also fixed to radial arms 13. An ignition device is provided in body 20 to produce ignition of the fuel mixture flowing therethrough. The slots for the pilot flames are shown at 4a.

The present invention makes it possible to obtain the following advantages which have been verified experimentally.

It is possible to ignite the pilot device independently whatever be the speed of the main stream of fuel mixture for a range of velocities extending from 0 to 150 m. per second and even more.

Once the pilot device is in action, it is possible to achieve a stable main combustion for richnesses (this term meaning the ratio of the amount of fuel to the amount corresponding to the stoichiometric ratio) ranging from $5 to values with above one.

Short main flames are obtained with an excellent combnstion efiiciency.

The pilot device can withstand the thermal stresses to which it is subjected.

In a general manner, while I have, in the above description, disclosed what I deem to be practical and eflicient embodiments of my invention, it should be well understood that I do not wish to be limited thereto as there might be changes made in the arrangement, disposition and form of the parts without departing from the principle of the present invention as comprehended within the scope of the accompanying claims.

What I claim is:

1. A continuous flow thermal engine which comprises, in combination, a casing of at least approximately cylindrical shape the front end of which forms a comburent gas intake, a streamlined hollow body in said casing disposed longitudinally therein at a distance from the inner wall thereof, a plurality of fuel injectors mounted in the space between the inner wall of said casing and the outer wall of saidbody, said fuel'injectors being lo cated downstream of the front end of said body, and upstream of the rear end thereof, means for at least partly closing the front end of said body, means for forming in said hollow body a pilot fuel and comburent mixture and means in said hollow body for igniting said last mentioned mixture, the side wall of said hollow body being provided, downstream of said injectors, with a plurality of longitudinal slots opening directly into said space between said body and said casing, the spaces between the slots being substantially greater than the width of the slots whereby there is obtained through each of said slots a pilot flame in the form of a sheet issuing therefrom into said space in a direction radial with respect to said body.

2. An engine according to claim 1 further including two outwardly extending radial fins along the longer edges of each of said slots, said two fins being substantially parallel to each other and entirely unconnected with each other.

3. An engine according to claim 1 in which said casing and said body are of revolution and coaxial with each other and the length of each of said slots is at least equal to the diameter of said body in a plane transverse thereto and located at the front end of said slot.

4. An engine according to claim 1 in which said injectors consist of radial fuel conduits extending inwardly from said casing, said conduits being provided with frontward outlets directed at angles of substantially 60 with respect to the axial planes passing through each of them.

5. A continuous flow thermal engine which comprises, in combination, a tubular casing the front end of which forms an air intake, a streamlined hollow body longitudinally mounted in said casing so as to leave a free space between the inner wall of said casing and the outer wall of said body, a plurality of fuel injectors mounted in said space, said fuel injectors being located downstream of the front end of said body, and upstream of the rear end thereof, the front end of said body being open to form an air intake, means for at least partly closing said front air intake of said body, means for feeding fuel to the inside of said body so as to form therein a pilot fuel and air mixture and means in said hollow body for igniting said last mentioned mixture, the side wall of said hollow body being provided, downstream of said injectors, with a plurality of longitudinal slots opening directly into said space, the spaces between the slots being substantially greater than the width of the slots the total area of said slots being at least equal to five times that of said air intake of said body, whereby there is obtained through each of said slots a pilot-flame in the form of a sheet issuing therefrom into said space in a direction radial with respect to said body.

6. A continuous flow thermal engine which comprises, in combination, a casing of at least approximately cylindrical shape the front end of which forms an air intake, a streamlined hollow body of circular cross section mounted in said casing coaxially therein so as to leave an annular space between the inner wall of said casing and the outer wall of said body, a plurality of fuel injectors mounted in said annular space, said fuel injectors being located downstream of the front end of said body, and upstream of the rear end thereof, the front end of said body being open to form an air intake, means for at least partly closing said front air intake of said body, means for feeding fuel to the inside of said body so as to form therein a pilot fuel and air mixture and means in said hollow body for igniting said last mentioned mixture, the side wall of said hollow body being provided, downstream of said injectors, with a plurality of longitudinal slots opening directly into said annular space, the spaces between the slots being substantially greater than the width of the slots whereby there is obtained through each of said slots a pilot flame 7 in the form of a sheet issuing therefrom into said space in a direction radial with respect to said body.

'7. An engine according to claim 1 including hollow streamlined radial arms interposed between said hollow body and said casing, the leading edges of said arms being provided with air intakes and said arms having their inner ends opening into said hollow body.

"8. A turbo-jet engine according to claim 1 including an air compressor, hollow radial arms interposed 'between said casing and said hollow body, and means for connecting the outlet of said compressor with said radial arms, the inner ends of said radial arms opening into said hollow body.

9. An engine according to claim 1 in which said hollow body includes a rear pointed end, a front endpin line with said rear end, and a plurality of gutter-shaped elements interposed between said front and rearends so as to define said slots, the whole of the bottom portions of said gutter-shaped elements forming the intermediate part of said hollow body between said front andrear ends. i

7 References Cited in the fileaof this patent UNITED STATES PATENTS 2,529,506 Lloyd et al. Nov. 14, 1950 2,625,788 Neikirk et al. Jan. 20,1953 2,640,321 Pouchot June 2,1953 2,679,137 Probert May 25, 1954 2,701,444 Day Feb. 8,1955 2,720,753 Sharpe Oct. 18, 1955 2,729,059 Fonre et al. Jan. 3, 1956 2,734,341 Lovesey Feb. 14, 1956 2,806,356 Bocehio Sept. 17, 1957 F GN P TEN S 1,088,309 France Mar. 7, 1,955 

